A U.S. marshal gestures to a crowd of journalists and people who were evacuated from the John Joseph Moakley United States Courthouse back during a bomb threat in Boston on Wednesday. Security officials reopened Boston's federal courthouse building to employees on Wednesday afternoon after an hour-long evacuation tied to a security scare. (REUTERS/Jessica Rinaldi)

False reports, fake threats keep the city, region on edge

McClatchy Newspapers

The FBI is seeking these men in connection with Monday's bombing at the Boston Marathon.

BOSTON - Investigators plugged away Wednesday in the search for the Boston Marathon bomber, or bombers, as they picked through videotape and explosive fragments with an expertise honed on foreign wars and terrorist attacks.

Investigators were able to reduce the size of the crime scene while they continued to search for debris behind barricades. Boston's heavily trafficked Boylston Street was reopened, even as investigators scrutinized videotape taken from a nearby Lord & Taylor department store that reportedly captured an image of one of the bombs, inside a black bag, being set down.

"The full weight of the federal government is behind this investigation," White House spokesman Jay Carney said. "We will find out who did this, we will find out why, and we will bring those responsible to justice."

President Barack Obama is scheduled to arrive in Boston today for an 11 a.m. interfaith service to honor the victims at the Cathedral of the Holy Cross, 1400 Washington St.

The FBI scheduled a briefing for 5 p.m. Wednesday, but postponed - then subsequently canceled - it, several hours after CNN and some other news agencies, citing anonymous government sources, inaccurately reported that a suspect was in custody.

Shortly afterward, security officials at Boston's federal courthouse ordered staff, media and attorneys to evacuate due to a bomb scare that was later found to be a false alarm.

Monday's blasts near the finish line of the marathon killed three, including 8-year-old Martin Richard, and injured at least 176 others. Physicians have performed multiple amputations on victims, whose ages range from as young as 2 to as old as 78.

The dual blasts sent fragments of glass, plastic, metal and other materials rocketing into victims' bodies, physicians reported Wednesday, with some evidence that the shrapnel included nails and BB-like pellets that might have been placed inside the weapons to boost their lethality.

"We are not making any judgment about where these fragments came from," Dr. Peter Burke, chief trauma surgeon at Boston Medical Center, told reporters at a Wednesday morning briefing. "It doesn't really matter to us. We are just dealing with the consequences of those fragments."

Boston Medical Center by Wednesday continued to treat 18 of the 19 marathon patients admitted Monday, with two of the patients still in critical condition. Eleven of the original 35 patients remain at Brigham and Women's Hospital, with four listed in critical condition. Eleven patients remain out of 31 admitted to Massachusetts General Hospital, four of them listed as critical. Beth Israel Deaconess Medical Center reported having 13 patients remaining out of 24 who were admitted.

Investigators have indicated they believe the bombs were constructed using pressure cookers, a tactic that counterterrorism agencies have found in the past in jihadist plans and "recipes." The bombs, though lethal, were neither complicated nor difficult to build.

"There's nothing particularly sophisticated about this attack," said Scott Stewart, a former special agent with the U.S. State Department, who said materials for such a bomb could be purchased in an afternoon.